The present invention relates to a device for felling and gathering trees and, more particularly, to a vehicle that is capable of operating on relatively steep slopes without danger of upsetting, thus increasing the safety and decreasing the cost of operation of such machines while expanding the area over which it can operate.
In the past, large trees have been logged from an area using yarders or skidders for moving trees out of a given area to a landing. In the past, trees were separately felled by saws and were usually attached one at a time or in bunches for delivery to the landing. Second and third growth timber, which is comprised of trees that are smaller and of more uniform size than virgin timber is now being logged. This has allowed a change in logging practices whereby a single machine can fell one or more trees and bunch several trees together for more efficient delivery to the landing.
Accordingly, a new class of vehicle referred to as a feller-buncher has been created to fulfill the need in the logging industry to fell generally uniformly sized trees to bunch them together in preparation for transport. Many of these vehicles generally comprise an articulated arm that is mounted on a platform, which is in turn mounted on a turntable that can rotate 360 degrees relative to the chassis upon which the turntable is mounted. Early feller-bunchers had the platform mounted rigidly to the frame, causing a significant shift of the center of gravity of the machine when it attempted to operate on steep slopes, thus limiting the extent to which the articulated boom could be extended beyond the chassis, especially in a downhill direction. More recent feller-bunchers have the turntable mounted on a trunnion system that allows the platform and an associated counterweight to be moved in a direction opposite to the angulation of the chassis relative to the horizontal, thus maintaining the cab and counterweight in an upright position and shifting the center of gravity back toward the center of the vehicle. Because of chassis design and other limitations in prior feller-bunchers, however, only limited success has been met in shifting the center of gravity so that operation over a wide variety of steep terrain can still be maintained. Moreoever, prior feller-bunchers have not incorporated systems whereby the operators are given an indication that tipping of the machine is imminent, or that incorporate systems that can, to a large degree, prevent the device from being operated in a mode that would allow it to tip. There has also been a need to develop more sophisticated suspensions and suspension control systems so that the machines can be operated efficiently and safely not only on steep hill sides, but on terrain that is very uneven and replete with obstacles.